The invention relates to equipment for the retardation of an inflow in circular or polygonal sedimentation tanks, final sedimentation tanks, and thickeners in sewage treatment plants, including a cylindrical or polygonal self-supporting structure around the central inlet, reaching from the liquid surface down the liquid depth, embodied by a retardation center well and one or more floats.
The uniform distribution and retardation of the inflow inside a circular flow section near the inlet structure is the most essential condition for the undisturbed flow in circular or polygonal sedimentation tanks for the resulting separation of solids and liquid. The effect of the separation is a physical-hydraulical function of the liquid surface available, the xe2x80x9cfree surfacexe2x80x9d. Therefore the surface of the tank or of the liquid should be as large as possible and should not be more restricted than necessitated by any structures, i. e. the above mentioned equipment. The equipment itself for the uniform distribution and retardation of the inflow must be large enough to comply with that other demand to produce the uniform flow. Demand for a large surface for uniform distribution is contradictory to demand for a large free surface in the tank for efficient sedimentation.
The German Patent Application DE 197 58 360 A1 describes a process and equipment for the separation of a mixture of clarified sewage and activated sludge. The inlet pipe is routed under the tank to its center with a vertical riser concentric to the tank wall. A cylindrical well is arranged in the upper region and concentric to the riser. The cylindrical well is provided with openings at different levels. Technical means allow to select the openings the most appropriated. The level of the inlet flow can be chosen by using different openings to achieve an optimized entrance of the mixture into the tank and penetrating the sludge layer. The level of the inlet flow can be adjusted depending on various parameters of the mixture and of hydraulic and other conditions in the operation. The use of different inlet elevations and flow volume are determined by water/sludge separation phases as well as the elevation of different concentration elevations in the tank. In this application the separation efficiency should be respected with the different flow rates and levels of the inlet opening only. The geometry of the inlet pipe and cylindrical well arc similar to the modifications of the German Patent Applications DE 195 43 462 A1 and DE 35 40 606 A1. A sufficiently retarded inflow cannot be attained using the means shown in those applications.
There arc innumerable other designs of inlet structures developed to get a solution for the above mentioned contradictory demand. These well known inlet structures do not sufficiently provide the desired calm and uniform flow.
The object of the invention refers to at least two steps:
My numerical simulations show efficiency can be achieved through larger and deeper structures of the inlet into the liquid. But such larger equipment can only be executed by a relatively great expenditure, which is unacceptable in most cases. Therefore the practical use of very large sizes of the equipment is impeded by geometry of location.
The object of the invention is to provide equipment to solve the large structure problem described above, to allow larger inlet structures also with conventional large tank sizes.
The objective of this invention is achieved by providing a cylindrical or polygonal self-supporting retardation center well around the central inlet reaching from the surface into the liquid and by providing one or more floats.
Another objective of this invention is achieved by providing the center well as a light weight structure and another objective is achieved by annular or polygonal floats.
Further advantage can be achieved and various structural designs are possible according to the features of the claims.
The use of floats is very common in the engineering. The German Patent Application DE 35 40 606 A1 shows voluminous packages of lamellas inside of a tank carried by floats. Within the spaces below and above the packages large mechanical structures revolve, i.e. scraping arms and rotating bridges. Therefore the voluminous packages of lamellas can only be carried by floats. They are additionally fixed at the wall of the tank. This complete unit is very heavy and not at all a light weight structure.
On the other side floats are known in water engineering to fix, to hold or to guide equipment at or corresponding to the water level, i. e. a floating scumboard in front of an outlet of a tank, according to German Patent DE 29 33 057 C2.